This invention relates to steam turbines used for power generation and, more specifically, to a gage used for measuring turbine rotor and packing clearances.
The interpretation of the results of performance monitoring activities can be used to identify turbine internal problems that may cause a deterioration in performance, and to assist in planning maintenance required to address the problems. However, to restore performance during a turbine maintenance outage, the turbine components contributing to the performance loss need to be identified. This can best be done by conducting a turbine steam path evaluation.
A steam path evaluation generally includes a detailed visual inspection of the steam path components and clearance measurements of the pickings and bucket tip spill strips. The visual inspection is used to evaluate and quantify the performance impact of degradation effects such as erosion, deposits, damage, preening, etc. Clearance measurements at multiple circumferential positions of the diaphragm packings, tip radial spill strips, and end shaft packings are used to quantify the effect of increased clearances. With this information, decisions can be made based on the economics associated with the repair and replacement of turbine components, and the priority of necessary repair work.
Conventional gages used to make the required clearance measurements during steam path evaluations have not been completely satisfactory. One such gage indicates measurements in 0.005 inch (5 thousandths) increments. These gradations are not sufficiently precise and oftentimes result in the operator making a guess at the measurement, or taking additional measurements with a feeler gage and then using a micrometer to determine the final measurement. In addition, the gage is not flexible and does not always fit into (or cannot reach) the areas needing measurement.